So you trust every cheap IoT device connected to your local network? The LAN may be a slightly less chaotic environment than the open Internet, but that doesn't make it "safe". With a bit of ARP trickery any device on the LAN can intercept traffic intended for any other local device and carry out an active MitM attack—and with HTTP you don't even get the benefit of "trust on first use" that you'd get with a persistent self-signed certificate.

Except for the browser complaint when filling out the form.

I have to agree with the calls for allowing warning-less HTTP for LAN connections.

Edit: Add last sentence.